void x(void);
void perm(int n, char a[n]){
  // This routine permutes the n characters starting at a and for
  // each permutation, calls x.
  // The characters are finally left as they were found.
  char t = a[0]; int j=n; while(j--) {
    char u = a[j]; a[0] = u; a[j] = t;
    if(n<3) x(); else perm(n-1, a+1);
    a[j] = u;} a[0] = t;}
typedef unsigned long int P;
#define C const
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
char u[16];
P cn = 0, cx=0;
char C * C a = "0123456789abcdef";
P sw[] = {0x0123456789ABCDEF, 0x021346578A9BCEDF,
0x041526378C9DAEBF, 0x08192A3B4C5D6E7F, 0x123C485A697BDE,
0X14283A596C7DBE, 0X24356879ACBD, 0X36587A9C, 0X3456789ABC, 0};
void x(){char y[16]; memcpy(y, u, 16);
P * c = sw; while(*c){P p = *(c++); while(p){int j = p&255;
  p >>= 8; if(j) {int k = j&15, i = j>>4;
    if(y[i]>y[k]){char t = y[i]; y[i] = y[k]; y[k] = t;}}}}
if(memcmp(y, a, 16)) {if(0) ++cn; else {
{for(int j = 0; j<16; ++j) printf ("%c%c%c ", u[j], y[j], a[j]);}
exit(printf("Foo\n"));}}
if(!(cx++& ((1L<<20)-1)))printf("%s %ld %ld\n", u, cx>>20, cn);}

int main(){memcpy(u, a, 16);
  perm(16, u);
  printf("%ld errors\n", cn);
  return 0;}